The present invention relates generally to electrostatic paint spray guns, and more particularly to electrostatic spray guns of the type developing an internal high voltage in circuitry which steps up a relatively low voltage generated by a rotating generator, wherein the generator is driven by an air turbine. The present invention particularly relates to an improvement in providing controlled pressurized air to the spray gun for the purposes of driving the air turbine, cooling components within the gun and exhausting the pressurized air with minimum noise.
Electrostatic paint spray guns have been recently developed and invented utilizing the concept of a primary power source being derived from a rotating air turbine member. Such a gun is described in U.S. Pat. Nos. 4,377,838, 4,219,865, and 4,290,091, and reference may be had to these patents for a detailed understanding of the theory of operation of guns of this type. Air turbine electrostatic spray guns require a source of pressurized air to be delivered to the gun, typically at pressures ranging from 30-60 pounds per square inch (psi). Prior art spray guns have utilized a pressurized hose attached to the handle of the spray gun, wherein the pressurized air is delivered through internal conduits to impinge upon turbine blades which are rotatable under the influence of this air. The exhaust air from such spray guns has been typically passed through the rear of the spray gun through a suitable muffler to reduce the audible noise produced by such air.
Air turbine electrostatic spray guns typically have a mechanically coupled electrical generator attached to a rotatable turbine, the generator generating a low voltage alternating current (AC) signal which is stepped up to an intermediate high volage AC signal through an oscillator and transformer circuit, coupled to a cascade voltage multiplier of the Cockcroft-Walton type. The cascade voltage multiplier is usually designed to develop an output DC voltage in the range of 50,000-80,000 volts.
The process of converting pressurized air input into this high voltage energy results in certain energy losses which produce heat inside of the spray gun. The spray gun body is typically constructed of an insulated plastic material, which is also a good heat insulator, and the internal heat generated by the mechanical and electrical components is not readily radiated from the gun. Excessive heat build-up can damage or destroy the mechanical and electrical components therein, and therefore care must be taken in designing such spray guns to provide means for dissipating the heat. The problem of internal heat build-up is further complicated by the need for reducing the overall physical size of the spray gun so that it may be manufactured in a compact package for easy handling by an operator. It is also desirable to make the gun as light in weight as possible, all of which makes it difficult to design into the gun the appropriate metallic heat conductors which might otherwise draw heat from the electrical components. The problem of removing excessive heat from such spray guns is addressed by the present invention, while at the same time controlling the air flow rate and minimizing the audible noise caused by the exhaust of the pressurized air supply to the gun.